Cal Amp VIPER SC+ 100 series User Manual - page 195
Viper SC+™ IP Router for Licensed Spectrum PN 001-5008-000 Rev. C
| Page 185
PLC communication via serial lines or serial terminal server is not covered here. Nevertheless, some of the information
could apply.
Note: Please consult information about general PLC setup presented earlier in this appendix for background
information about systems with PLC setup.
ALLEN-BRADLEY MICROLOGIX 1100 OR 1400 (MAY ALSO APPLY TO SLC 5)
Following are important settings recommended to improve communication when used with a limited bandwidth Viper
network. This provides more specific information that supplements the general PLC communication information
presented earlier in this appendix..
Note: When required, contact your PLC provider or Allen-Bradley or Rockwell Automation support.
PLC Ladder Logic On Restart Opens All Connections At Once Instead Of Sequentially
When the PLC ladder program is set up to have at startup all write message rungs set to true, all TCP connections are
triggered “simultaneously.” This creates an overload of TCP SYNs and somewhat could congest the on-air traffic
depending on the system.
It is recommended to setup the ladder write message rungs not to start up simultaneously. Write messages should be
setup to open the TCP connection sequentially. For more information it may be required to contact your PLC provider
or Allen-Bradley or Rockwell Automation support.
PLC Sends Too Many “CIP Forward Open” and “CIP Forward Close” Messages
After the TCP connection is first established, then the CIP Forward Open command is sent to open the CIP connection.
As long as there is always communication activity over that connection within eight times the Message Apply timeout
of channel 1, there will be no more CIP Forward Close commands sent (this results in fewer messages sent over the air,
which is good).
Often the Channel 1 Message Reply timeout is set to 3000 milliseconds. This would generate additional CIP Forward
Open and CIP Forward Close messages on-air if the polling interval exceeds 3 sec × 8 = 24 seconds.